This invention relates to quick-acting fluid valve assemblies coupled to fluid jet cutting nozzles. Within the prior art, a wide variety of known valve configurations is available for use in regulating fluid flow. However, within the context of fluid cutting jet technology, suitable valve structures have not yet attained a level of reliability to guarantee their success on a commercial scale.
Fluid jet cutting utilizes a fine, shaped beam of fluid emanating through a jewel nozzle at approximately 40,000-60,000 psia. The cutting fluid is typically water which passes through an intensifier to generate the pressures for cutting. Accordingly, any valve which is to be utilized in the context of fluid jet cutting must be able to accommodate high-pressure fluid input without degradation of the valve structure itself. At high pressures, in the range of 40,000-60,000 psia, problems of leaching of the valve stem are quite common. Because most prior art valves utilize conventional steel stems, the impact of high-pressure fluid will tend to erode or leach the steel away, creating leaks in the valve structure. Additionally, the valve seat which is not particularly yieldable will tend to leach or otherwise deform under the impact of high-pressure fluid as it passes from the fluid input to the expansion section, thereby creating an imperfect seal structure between the seat and stem. Accordingly, prior art valve systems have proven unreliable over long cycle lives because of a propensity to develop leaks at the stem and seal point.
Replacement of valves is a costly, time-consuming procedure which reduces throughput of fluid cutting jet systems. Typically, the operating life objective of such a valve has been established in the range of 250,000 cycles. This stringent requirement is necessitated by the fact that the remainder of a fluid jet cutting system is generally maintainable over a comparable duty cycle lifetime, and accordingly, the valve should at least maintain that same level of reliability. Also, such valves should be capable of quick maintenance with a minimum of time and expense.
Moreover, valve assemblies used in fluid jet cutting are required to cycle--i.e., that is, supply then cut-off water within very short cycle times, typically about 3 seconds. Typically, cycling time in the range of 75 milliseconds is required so that it does not effect the throughput of the machine. Such short cycling is required because the fluid jet cutting is under the control of a computer, and as the cutting operation proceeds, throughput of the machine is a function of the ability of a fluid jet valve to cycle in response to cutting commands. Although many fast-acting valve arrangements are known, none is commercially known and available which combines a 25 millisecond cycle time together with the ability to control 60,000 psia fluid. The reliability requirements imposed in fluid jet cutting, together with use considerations--namely, high-pressure water and fast duty or cycle time--have made prior art valve arrangements unsuited for use in fluid jet systems.
Another problem existing in prior art devices, common in quick-reaction valves, is a propensity of leakage of the working fluid, primarily hydraulic fluid or oil, with the regulated fluid, in this case water. After repeated cycling, contamination and breakdown of a valve seal used to isolate the stem from the switch section of the valve tends to occur, thereby resulting in a leakage of hydraulic fluid into the regulated fluid. This problem is acutely present in situations where high-pressure fluid is utilized for purposes of regulation since breakdown of the seal at the stem portion is a function of deformation and leaching as a result of the influence of such high-pressure fluid.
Accordingly, there has existed within the field of fluid jet cutting a necessity for a valve assembly which has a rapid cycling time--in the order of 25 milliseconds--yet maintains the ability to cycle and regulate high-pressure water in the range of 60,000 psia over a duty cycle lifetime of approximately 250,000 cycles. Also, in view of the high pressures involved, extreme safety requirements must be met to isolate the cutting fluid when the hydraulics are off--i.e., the valve must be maintained in a normally closed position.